Radiant heating units



March 23, 1965 R. L. JONES ETAL RADIANT HEATING UNITS 2 Sheets-Sheet 1Filed Oct. 4, 1963 Q INVENTORS -M z. 90" BY 7M u 21444 ON N March 1965R. L. JONES ETAL RADIANT HEATING UNITS 2 Sheets-Sheet 2 Filed 001;. 4,1963 INVENTORS EM 1 W.

4 I, 41A MC Q C ZW United States Patent 3,174,474 RADIANT HEATING UNITSRobert L. Jones and Howard H. Nichols, Pittsburgh, Pa, assignors toHazen Engineering Company, Pittsburgh, Pa, a corporation of PennsylvaniaFiled Oct. 4, 1963, Ser. No. 314,840 Claims. (Cl. 126--91) Thisinvention relates to new and useful improvements in radiant heatingunits, more particularly to a self-contained gaseous fuel combustionunit in which the combustion chamber is the space between a metalhousing and a combustion air tube disposed within said housing and fuelis supplied by a pipe extending centrally through said combustion airtube; the heat generated being radiated from the housing wall to thearticles or chamber being heated without any products of combustionescaping to the heating chamber. The present application is acontinuationin-part of an application serially numbered 122,591, filedJuly 7, 1961, which application has been abandoned.

It is among the objects of this invention to provide a radiant heaterunit having a closed housing portion of tubular elliptical or othershape mounted on and extending from a wall or between spaced walls of aheating chamber, one or both ends of the housing extending outside saidwalls and having a combustion air tube projecting substantially the fulllength into the housing and in which one end of said tube may be securedto the outer end of the housing to form a closure therefor.

It is still a further object of the invention to provide a method offiring radiant heating units in which a mixture of gaseous fuel andpreheated air is directed to the end of a combustion chamber and causedto reverse its direction of flow while burning in said chamber and byadding air preheated to combustion temperatures at intervals into thepath of flow of said burning mixture combustion is maintained throughoutthe length of the combustion chamber.

Heretofore radiant heating units utilized a primary burner at the closedend of the tube to which a combustible mixture of fuel and air wascontinually supplied and in some instances supplemental air wasdelivered to the combustion chamber surrounding the air tube to controlor regulate combustion along the length of the tube.

In accordance with the present invention, pro-mixed air and fuel arecaused to flow through an annular combustion chamber and pro-heated airfrom a series of perforations or air ports in an air tube pierces theflow of the combustible gases causing a jet-like flame that completelyburns the adjacent combustible mixture which is inspirated into the airstream and any excess combustible mixture by-passes the flame and goesto the next perforation to be consumed in the presence of the secondaryair from the air tube orifice. These burner flames are the reverse of anordinary Bunsen burner flame because there is no primary combustion asin conventional tube heaters.

The invention will become more apparent from a consideration of theaccompanying drawings constituting a part hereof in which like referencecharacters designate like parts and in which:

FIGURE 1 is a vertical section taken longitudinally of a radiant burnerunit embodying the principles of this invention;

FIGURE 2 is a cross-sectional view taken along the line 2-2, FIGURE 1;

FIGURE 3 is a view diagrammatically illustrating the flamecharacteristic of the hot pre-mixed air and gases burning in thecombustion chamber;

FIGURE 4 is a diagrammatic illustration of an annealing chamberutilizing the radiant heating units for the an.- nealing of sheet steelor strip that continuously passes through said chamber;

FIGURE 5 is a vertical section taken longitudinally of a radiant burnerunit as in FIGURE 1, in which the tube is disposed between the spacedwall of a heating chamber; and

FIGURES 6 and 7 are diagrammatic views of air and gas inspirated'flames, respectively.

In the drawing, the numeral 1 is a housing supported in a furnace wall 2by means of a clamping ring 3 and a sealing material 4. The housing 1 isnot supported at its extended end that projects into the furnace chambersuch as an annealing chamber for annealing steel sheets or strip,designated by the numeral 5 in FIGURE 4 of the drawing, the numeral 1designating a plurality of the radiant heating units of FIGURE 1 as theyare arranged for continuous annealing of the strip shown in FIGURE 4.

The housing 1 has a closed end 6 and is provided with a waste gas exitpassage 7. An inner tube, or what may be termed a combustion air tube 8,is disposed within the housing 1 and is open at 9 and provided with aflared end 10 at its other end. The end 10 is provided with a flange 11that seats against a sealing material 12 carried by a mounting bracket13.

In the construction so far shown, it will be evident that if the wastegas passage 7 is connected to a fan, the combustion chamber between thehousing 1 and tube 8 that is designated by the numeral 14 may beexhausted or evacuated. However, when a fan is so applied, air will bedrawn in through the funnel-shaped opening designated by the numeral 15,and drawn from the mouth 9 of the inner tube into the chambersurrounding that tube, which is the chamber 14.

The inner tube 8 is held in position by spacer lugs 16, of which thereare four shown in FIGURE 2 of the drawing, the lugs being spacedlongitudinally within the housing, as shown in FIGURE 1.

Disposed Within the combustion air tube 8 is a tube 17 connected to asource of fuel gas. The tube runs to substantially the end of thecombustion air tube 8 and de ivers fuel gas to mingle with the air drawninto the opening 15 when both the fuel and air reach the end of the tube8. This combustible mixture may be ignited in any suitable manner as bya spark plug 18 located at the exhaust end of the combustion housing,FIGURE 1, or at the closed end shown in FIGURE 5. The fuel gas tube 17is provided with spacers 19 to center the tube with the combustion airtube 8, as shown in FIGURE 2. The combustion air tube 8 is provided witha series of perforations 20 that are spaced longitudinally of thecombustion air tube 8, as shown in FIGURE 1. These perforations may besupplied in any number and spaced in any manner, they being shown inangularly spaced relation in FIGURE 2. It is apparent, however, thatthey may be spaced in a helical path for reasons to be hereinafterexplained.

As shown in FIGURE 2, the housing 1 is of elliptical shape, while thecombustion air tube 8 is of cylindrical shape, as is also the gaseousfuel tube 17. The spacers 16 and 19 maintain the combustion air and fueltubes in proper spaced relation to each other and with the outer housing1.

Fuel gas is supplied through the tube 17 to the end of the fuel tube,which is adjacent the end of the combustion air tube 8, as shown inFIGURE 1. There is a small deflector plate 21 secured to the end of thecombustion air tube 8 by spaced lugs 22. Also a small tubular portion17a is mounted in spaced relation with the gaseous fuel tube 17 near theend of said tube to draw the combustion air from the space 23 betweenthe combustion air tube 8 and fuel gas tube 17 into the mixing end orchamber 9 of the tubes to form a mixture of air and gaseous fuel thatwill burn in the presence of secondary air, said secondary air ismetered into the above mixture through the perforations 20 as it flowstoward the exhaust end of the combustion chamber 14.. The

combustible mixture, in the combustion chamber 14, is ignited by thespark plug 18. The regulation of the exhaust controls the rate ofcirculation for flow of the gas air mixture and the products ofcombustion resulting therefrom. The perforations 20 along the path offlow of this mixture supplies preheated air to the mixture to supportsecondary combustion and the outer housing 1 becomes substantiallyuniformly heated over the area exposed to the Work.

The preheated fuel gas with air preheated to substantially combustiontemperature is delivered at the closed end 6 of the housing and flowscounter to the air and gas flow through the annular combustion space 14to the outlet 7, as shown by the arrows in FIGURE 1 of the drawing, andas the pre-mixed fuel and air passes through the annular chamber 14, itis pierced by high velocity streams of preheated air at each of theperforations 20. The resulting flame may be termed a reverse flamebecause the air cone is inside and the fuel and air pre-mix is on theoutside of the flame. The flame at each perforation 2G consumes theavailable fuel and any excess fuel by-passes the flame and goes to thenext perforation to be consumed in the presence of the secondary airfrom the adjacent orifice 20. There is no mixing of the air and fuel atthe orifices 20 because they merely supply air and there is a completefire at each orifice point.

Conventional gaseous fuel burners are of the Bunsen burner type, asshown in FIGURE 6 of the drawing. In this case, the flame exists in amedia of secondary air and the gas velocity through the port mustinspirate enou h of this secondary air to complete combustion of all ofthe gas passing through the port 20. The volume of secondary airrequired usually exceeds the volumeof the gas by several hundredpercent, depending upon the percentage of combustibles in the gaseousfuel. In FIG- URE 6, the reference numeral 30 designates an area ofcombustible gas in the form of a burner flame and the flame-shaped area31 designates the inspirated air enveloping the gaseous mixture tocomplete combustion of the gas passing through theport 20. In otherwords, the flame-shaped fuel area 30 is projected into a normalatmosphere to ignite in the presence of the oxygen in the air. When thistype of flame is employed in a tight closure, the products of combustionfrom the flame contaminate the secondary air media reducing the oxygencontent. It does not take very much of a reduction of this oxygencontent to upset the characteristic of the flame and with a little morecontamination of the media, the flame goes out, assuming there are aseries ofsuch flames in the path of travel of the secondary air media.

In FIGURE 7, the flame is shown as a flame-shaped cone 32 of preheatedair; namely, air preheated to substantially combustion temperaturesurrounded by a flameshaped area 33 of a combustible gaseous mixture. Inother words, the flame-shaped areas of preheated air are projected intoa combustible gaseous atmosphere which is the reverse of the Bunsen typeburner flame shown in FIGURE 6. Contrary to the contamination of the airthat sustains combustion of the flame in FIGURE 6 of the drawing, theproducts of combustion surrounding the flame in FIGURE 7 only reduce theB.t.u. content or the percentages of combustibles in the fuel gas mediainto which the preheated air is injected, as shown in FIGURE 7. Thispercentage of combustibles has to drop quite low before the velocity ofthe air stream cannot inspirate enough fuel to satisfy the oxygen of theair piercing the gaseous media above the port 20, FIG- URE 7. Theremainder is unsatisfied oxygen and not unburnt fuel, hence nocontamination of the secondary air media as occurs in the Bunsen burnertype of combustion.

It is thus evident that with a slight excess of air occurring when theflames exhaust in a very low percentage of combustibles, practically allof the fuel in the media can be burned in a tight enclosure such as in aradiant tube heater with the character of the flame remainingsubstantially constant.

Other advantages of the type of flame of FIGURE 7 are that the velocityof the air passing through port 20 can be fairly high before anyblow-off of the flame occurs, whereas in the flame of FIGURE 6 wherefuel gas passes through the port 20, blow-off occurs at a much lowervelocity and the type of flame shown in FIGURE 7 has a much higherradiation characteristic than the Bunsen burner type flame of FIGURE 6.In the type of flame produced as shown in FIGURE 7, the air is separatedfrom the products of combustion and each jet of air inspiratessufficient fuel to combine with all the oxygen in the jet of air fromport 20. Products of combustion dilute the remaining unburnt fuel butthe continuing piercing of the gas stream with multiple jets of airresults in complete combustion of the gaseous mixture passing across theburner flames.

Each row of holes completely burns the adjacent fuel which is inspiratedinto the air stream until the oxygen in the individual air stream isexhausted. Fuel passing around this cone of combustion mixes with theproducts of combustion from this particular flame and passes on to bepierced by the next row of holes. Each cone is sharp and distinct andcombustion at the last rows of orifices at the exit end of the tubetakes place in a very low B.t.u. gas content, but the temperature ofthis gas is high enough for combustion at this point.

This glowing radiant heat is transmitted to the continuous strip orsteel sheet passing over the guide rolls of FIGURE 4 in the annealingchamber, which is enclosed Within the walls 2 and 2a of the furnace. Ifthe perforations 20 are spaced to form a helix in the wall of thecombustion air tube 8, the gaseous fuel mixture and products ofcombustion will be directed to flow angularly in the combustion chamber14. This would give the fuel mixture and products of combustion a longerpath of travel in its passage through the combustion chamber.

The return or exhaust of the fan can be regulated by placing athermostat 25 in the wall of the combustion air tube, as shown in FIGURE2, and the thermostat may be connected by conductors 26 and 27, FIGURE1, to an electric control circuit for regulating the fan or blowerspeed.

It is, of course, evident that instead of an exhaust fan connected tothe waste gas exit 7, the open mouth or inlet passage 15 may beconnected to a blower and air forced under pressure through thecombustion air tube 8 to the end of the tube and thence into thecombustion chamber 14 from which it exits from the passage 7. Whetherthe air supply is under pressure or by suction is immaterial to theoperation of the device, as it will function the same either way. I

It is evident that the injection of the air preheated to combustiontemperatures into the hot pre-mixed air and gas, produces an intenseheating flame in the combustion chamber adjacent the point of injection.This is plainly visible on the outside of the housing 1, which is moreintensely heated adjacent the air holes or perforations than in otherareas of the housing.

As shown in FIGURES 1 and 5, the ignition means such as the spark plug18 may be located at any portion of the combustion tube, it being shownat the exhaust end in FIGURE 1 for convenience so that it is outside ofthe heating chamber where it would not be exposed to the heat of thechamber. Similarly, in FIGURE 5 the spark plug 18 is shown outside ofthe chamber but at the closed end of the tube. It could also be locatedat the center or any other part of the tube for the reason that theseparate flames will be propagated successively from the point ofignition because of the separate jets of air that support combustion. Aspreviously explained, the pre-mixed, preheated air and fuel is not acombustible mixture, per se,

as combustion takes place only at the air jets where sufficient oxygenis available to burn the pro-mixed air and fuel. Hence there can be noexplosion resulting from ignition.

Although one embodiment of the invention has been herein illustrated anddescribed, it will be evident to those skilled in the art that variousmodifications may be made in the shape of the housing, the relative sizeof housing and combustion air tube, the number and kind of spacing lugsand in the arrangement and number of air holes in the combustion airtube and other details of construction without departing from theprinciples herein set forth.

We claim:

1. In a radiant heating unit a housing forming a combustion chamberclosed at one end and having an exhaust passage for the products ofcombustion at the other end thereof, a tubular member having aperforated wall extending into said housing in spaced relation with theinner and end walls of said housing, said tubular member being open atits extended end adjacent the closed end of the combustion chamberhousing to conduct a gaseous medium into the space between the tubularmember and the closed end of the combustion chamber housing and throughthe perforations in the wall thereof, a second tubular member disposedin said first tubular member in spaced relation therewith having an openend adjacent and axially spaced from the open end of said first tubularmember, said second tubular member being adapted to conduct a gaseousmedium to the open end of said firstnamed tubular member to mix with thegaseous medium in said first-named tubular member and cause the same toflow around from the closed end of the combustion chamber through theannular space between the first-named tubular member and the combustionchamber wall to the exhaust passage of the combustion chamber, andignition means at the exhaust end of the combustion for igniting thegaseous mixture beginning at the perforations in the first-named tubularmember nearest the exhaust passage of the combustion chamber.

2. A radiant heating unit as set forth in claim 1 in which thefirst-named tubular member is an air tube and the second-named tubularmember a tube for supplying a gaseous fuel whereby the air from theperforations pierce the gas mixture flowing through the space betweenthe first tubular member and the combustion chamber wall to formignition points at each perforation.

3. A radiant heating unit as set forth in claim 2 in which the ignitionmeans at the exhaust end of the combustion chamber ignites the air andgas mixture at the per-foration nearest the ignition point.

4. The steps in the method of firing a radiant heating unit having ahousing forming a combustion chamber with an exhaust passage at one end,an air tube for delivering air with perforations opening into thecombustion chamber and open at the closed end of the combustion chamberand a fuel line in said air tube for delivering gaseous fuel to the openend of the air tube which comprises;

(a) delivering air under pressure through the air tube to the open endof the air tube and through the perforations in the wall thereof,

(b) delivering fuel under pressure to the open end of the air tube toform a gas mixture passing through the combustion chamber to the endopposite the entrance of the gas and air mixture by reversing the fiowof the gaseous mixture on the outside of the air tube,

(c) piercing the gas mixture flowing through the cornbustion chamber bythe air escaping from the perforations of the air tube, and

(d) igniting the gas mixture at the exhaust end of the combustionchamber to initially fire the gas mixture developed at the perforationof the air tube nearest the exhaust passage whereby the gaseous mixturesresulting from the air escaping from the perforations are progressivelyignited along the length of the air tube.

5. The steps in the method of firing a radiant heating unit having ahousing forming a combustion chamber closed at one end with an exhaustpassage at the other end and a perforated air tube and a fuel linedisposed therein having openings adjacent the closed end of thecombustion chamber which comprises:

(a) delivering air through the perforations of the air tube at avelocity to form air jets extending into the combustion chamber,

(b) delivering fuel under pressure to the open ends of the air tube andfuel line to form a gas mixture at the closed end of the combustionchamber to pass through the combustion chamber across the air jets tothe exhaust passage opposite the entrance of the gas and air mixture,and,

(c) igniting the gas mixture when combined with the air from the jets topropagate burner flames in the combustion chamber at the perforationsalong the length of the air tube.

References Cited by the Examiner UNITED STATES PATENTS 2,201,385 5/40Woodson 126-91 X 2,226, 816 12/40 Hepburn 126-91 2,255,540 9/41Dretfein.

FOREIGN PATENTS 556,136 4/57 Belgium. 502,1 12 3 39 Great Britain.537,657 7/41 Great Britain.

OTHER REFERENCES Hauck, German application S. N. 1,064,671, Sept. 3,1959.

JAMES W. WESTHAVER, Primary Examiner. FREDERICK KETTERER, Examiner.

1. IN A RADIANT HEATING UNIT A HOUSING FORMING A COMBUSTION CHAMBERCLOSED AT ONE END AND HAVING AN EXHAUST PASSAGE FOR THE PRODUCTS OFCOMBUSTION AT THE OTHER END THEREOF, A TUBULAR MEMBER HAVING APERFORATED WALL EXTENDING INTO SAID HOUSING IN SPACED RELATION WITH THEINNER AND END WALLS OF SAID HOUSING, SAID TUBULAR MEMBER BEING OPEN ATITS EXTENDED END ADJACENT THE CLOSED END OF THE COMBINATION CHAMBERHOUSING TO CONDUCT A GASEOUS MEDIUM INTO THE SPACE BETWEEN THE TUBULARMEMBER AND THE CLOSURE END OF THE COMBUSTION CHAMBER HOUSING AND THROUGHTHE PERFORATIONS IN THE WALL THEREOF, A SECOND TUBULAR MEMBER DISPOSEDIN SAID FIRST TUBULAR MEMBER IN SPACED RELATION THEREWITH HAVING AN OPENEND ADJACENT AND AXIALLY SPACED FROM THE OPEN END OF SAID FIRST TUBULARMEMBER, SAID SECOND TUBULAR MEMBER BEING ADAPTED TO CONDUCT A GASEOUSMEDIUM TO THE OPEN END OF SAID FIRST-